Abstract: The invention relates to a seal for a piston and a cylinder of a double-acting hot gas engine or other applications in which piston rings of plastic materials should be used.A duct having low resistance against gas flow is provided between the high pressure of the seal and the bottom of a groove for the piston ring. The resistance against gas flow between the high pressure side and the piston ring along the piston and cylinder walls is substantially greater. Thus the piston ring will immediately be forced into a sealing position when the engine is pressurized.

Abstract: Piston rod sealing means of the type in which oil is applied to the low pressure side (5) of the seal and used to prevent escape of high pressure gas between the piston rod (6) surface and a surrounding surface of a plastic material gland (12) are improved by providing the gland (12) with a tubular extension (15) of slightly increasing inner diameter in the direction against the high pressure side (4) of the seal. The gland (12) is forced against the piston rod surface, but the tubular extension (15) is not influenced by the force on the gland (12).